Fabricated wood I-joists are known and are commercially available. Generally such fabricated wood I-joists are often designed wherein a plywood web is supported between wood flanges. Typically the wood flanges are manufactured by gluing elongated wood laminates together. In manufacturing such wood flanges, it is common to find that the individual wood members or laminates are relatively thin and extend through a substantial span of the joist. Each individual wood member or laminate is secured to another wood laminate in face-to-face relationship by glue. Consequently the wood flanges are face glued. Therefore, to form a relatively large I-joist in cross section, many laminations are required and a substantial amount of glue is used. Further it is appreciated that a great amount of energy is required simply to make the laminates used in such I-joists. Because of this, such wood I-joists tend to be expensive and can involve complicated and time consuming manufacturing processes.
Moreover, in the manufacturing and construction of fabricated wood I-joists, little or no attention has been given to the selective use and location of various grade lumber to yield a more economical joist. In reality, laminated joists of the prior art have been manufactured with a single grade of wood laminate throughout. It is appreciated that this results in certain areas of the wood I-joist being structurally overdesigned with respect to the loading that such can be expected to carry. Thus, it is appreciated that this practice results in the wood I-joist costing more than would be required if the wood I-joist was designed such that higher grade lumber was only used in strategic areas that required such.
Given the fact that fabricated wood I-joists are being used and are going to continue to be used in construction, there is a need to develop new and improved design approaches that minimize total cost but which provide proper structural design.